Semiconductor device and method for fabricating the same

ABSTRACT

A method for fabricating semiconductor device includes the steps of: providing a substrate having a fin-shaped structure thereon; forming a single diffusion break (SDB) structure in the substrate to divide the fin-shaped structure into a first portion and a second portion; forming a first gate structure on the SDB structure; forming an interlayer dielectric (ILD) layer on the first gate structure; removing the first gate structure to form a first recess; and forming a dielectric layer in the first recess.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The invention relates to a method for fabricating semiconductor device,and more particularly to a method for dividing fin-shaped structure toform single diffusion break (SDB) structure.

2. Description of the Prior Art

With the trend in the industry being towards scaling down the size ofthe metal oxide semiconductor transistors (MOS), three-dimensional ornon-planar transistor technology, such as fin field effect transistortechnology (FinFET) has been developed to replace planar MOStransistors. Since the three-dimensional structure of a FinFET increasesthe overlapping area between the gate and the fin-shaped structure ofthe silicon substrate, the channel region can therefore be moreeffectively controlled. This way, the drain-induced barrier lowering(DIBL) effect and the short channel effect are reduced. The channelregion is also longer for an equivalent gate length, thus the currentbetween the source and the drain is increased. In addition, thethreshold voltage of the fin FET can be controlled by adjusting the workfunction of the gate.

In current FinFET fabrication, after shallow trench isolation (STI) isformed around the fin-shaped structure part of the fin-shaped structureand part of the STI could be removed to form a trench, and insulatingmaterial is deposited into the trench to form single diffusion break(SDB) structure or isolation structure. However, the integration of theSDB structure and metal gate fabrication still remains numerousproblems. Hence how to improve the current FinFET fabrication andstructure has become an important task in this field.

SUMMARY OF THE INVENTION

According to an embodiment of the present invention, a method forfabricating semiconductor device includes the steps of: providing asubstrate having a fin-shaped structure thereon; forming a singlediffusion break (SDB) structure in the substrate to divide thefin-shaped structure into a first portion and a second portion; forminga first gate structure on the SDB structure; forming an interlayerdielectric (ILD) layer on the first gate structure; removing the firstgate structure to form a first recess; and forming a dielectric layer inthe first recess.

According to another aspect of the present invention, a method forfabricating semiconductor device includes the steps of: providing asubstrate having a fin-shaped structure thereon; forming a singlediffusion break (SDB) structure in the substrate to divide thefin-shaped structure into a first portion and a second portion; forminga first gate structure on the SDB structure; forming a mask layer aroundthe first gate structure; removing the gate structure to form a recess;removing the mask layer; and forming a dielectric layer in the recessand on the fin-shaped structure around the recess.

According to yet another aspect of the present invention, asemiconductor device includes a gate structure on a fin-shaped structureand a single diffusion break (SDB) structure adjacent to the gatestructure. Preferably, the SDB structure includes a bottom portion inthe fin-shaped structure and a top portion on the bottom portion, inwhich the bottom portion and the top portion comprise differentmaterial.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-6 illustrate a method for fabricating a semiconductor deviceaccording to an embodiment of the present invention.

FIGS. 7-10 illustrate a method for fabricating a semiconductor deviceaccording to an embodiment of the present invention.

DETAILED DESCRIPTION

Referring to FIGS. 1-6, FIGS. 1-6 illustrate a method for fabricating asemiconductor device according to an embodiment of the presentinvention, in which FIG. 1 is a top view illustrating a method forfabricating the semiconductor device, left portions of FIGS. 2-6illustrate cross-sectional views of FIG. 1 for fabricating thesemiconductor device along the sectional line AA′, and right portions ofFIGS. 2-6 illustrate cross-sectional views of FIG. 1 for fabricating thesemiconductor device along the sectional line BB′. As shown in FIGS.1-2, a substrate 12, such as a silicon substrate or silicon-on-insulator(SOI) substrate is first provided, and a plurality of fin-shapedstructures 14 are formed on the substrate 12. It should be noted thateven though nine fin-shaped structures 14 are disposed on the substrate12 in this embodiment, it would also be desirable to adjust the numberof fin-shaped structures 14 depending on the demand of the product,which is also within the scope of the present invention.

Preferably, the fin-shaped structures 14 of this embodiment could beobtained by a sidewall image transfer (SIT) process. For instance, alayout pattern is first input into a computer system and is modifiedthrough suitable calculation. The modified layout is then defined in amask and further transferred to a layer of sacrificial layer on asubstrate through a photolithographic and an etching process. In thisway, several sacrificial layers distributed with a same spacing and of asame width are formed on a substrate. Each of the sacrificial layers maybe stripe-shaped. Subsequently, a deposition process and an etchingprocess are carried out such that spacers are formed on the sidewalls ofthe patterned sacrificial layers. In a next step, sacrificial layers canbe removed completely by performing an etching process. Through theetching process, the pattern defined by the spacers can be transferredinto the substrate underneath, and through additional fin cut processes,desirable pattern structures, such as stripe patterned fin-shapedstructures could be obtained.

Alternatively, the fin-shaped structures 14 could also be obtained byfirst forming a patterned mask (not shown) on the substrate, 12, andthrough an etching process, the pattern of the patterned mask istransferred to the substrate 12 to form the fin-shaped structures 14.Moreover, the formation of the fin-shaped structures 14 could also beaccomplished by first forming a patterned hard mask (not shown) on thesubstrate 12, and a semiconductor layer composed of silicon germanium isgrown from the substrate 12 through exposed patterned hard mask viaselective epitaxial growth process to form the corresponding fin-shapedstructures 14. These approaches for forming fin-shaped structure are allwithin the scope of the present invention.

Next, a shallow trench isolation (STI) 16 is formed around thefin-shaped structures 14. In this embodiment, the formation of the STI16 could be accomplished by conducting a flowable chemical vapordeposition (FCVD) process to form a silicon oxide layer on the substrate12 and covering the fin-shaped structures 14 entirely. Next, a chemicalmechanical polishing (CMP) process along with an etching process areconducted to remove part of the silicon oxide layer so that the topsurface of the remaining silicon oxide is slightly lower than the topsurface of the fin-shaped structures 14 for forming the STI 16.

After the STI structure 16 is formed, a single diffusion break (SDB)structure 18 is formed in the substrate to divide each of the fin-shapedstructures 14 into a first portion 20 and a second portion 22.Preferably, the formation of the SDB structure 18 could be accomplishedby conducting a photo-etching process to remove part of the fin-shapedstructures 14 for forming a recess, forming a dielectric layer into therecess, and then conducting a planarizing process such as CMP withoptional etching back process to remove part of the dielectric layer sothat the top surface of the remaining dielectric layer is slightly lowerthan the top surface of the divided fin-shaped structures 14. As shownin FIG. 1, the fin-shaped structures 14 are disposed extending along afirst direction (such as X-direction) and the SDB structure 18 isdisposed extending along a second direction (such as Y-direction), inwhich the SDB structure 18 preferably separates each of the fin-shapedstructures 14 into two portions, including a first portion 20 on theleft side of the SDB structure 18 and a second portion 22 on the rightside of the SDB structure 18.

It should be noted that even though the SDB structure 18 is formed afterthe STI 16 in this embodiment, the SDB structure 18 could also be formedat the same time with the STI 16, which is also within the scope of thepresent invention. If the STI 16 and the SDB structure 18 were formed atthe same time, the two elements would preferably be made of dielectricmaterial including but not limited to for example silicon oxide.Nevertheless, if the SDB structure 18 were formed after the STI 16, theSTI 16 would preferably be made of silicon oxide while the SDB structure18 could be made of either silicon oxide or silicon nitride. In otherwords, the STI 16 and the SDB structure 18 could be selected from thegroup consisting of silicon oxide and silicon nitride while the STI 16and the SDB structure 18 could be made of same material or differentmaterial depending on the demand of the process, which are all withinthe scope of the present invention.

Next, gates structures 24, 26, 28, 30, 32, 34, 36, 38, 40 or dummy gatesare formed on the fin-shaped structure 14 and the STI 16, in which theleft portion of FIG. 2 illustrates gate structures 30, 34 disposed onthe fin-shaped structure 14 and gate structure 32 disposed directly ontop of the SDB structure 18 while the right portion of FIG. 2illustrates a gate structure 36 adjacent to an edge of the fin-shapedstructure 14 and a portion of the gate structure 38 standing directly ontop of the STI 16. In this embodiment, the formation of the gatestructures 24, 26, 28, 30, 32, 34, 36, 38, 40 could be accomplished by agate first process, a high-k first approach from gate last process, or ahigh-k last approach from gate last process. Since this embodimentpertains to a high-k last approach, a gate dielectric layer orinterfacial layer, a gate material layer made of polysilicon, and atleast a selective hard mask could be formed sequentially on thesubstrate 12, and a photo-etching process is then conducted by using apatterned resist (not shown) as mask to remove part of the hard mask,part of the gate material layer, and part of the gate dielectric layerthrough single or multiple etching processes. After stripping thepatterned resist, gate structures 24, 26, 28, 30, 32, 34, 36, 38, 40each composed of a patterned gate dielectric layer 42, a patternedmaterial layer 44, a hard mask 45, and a hard mask 46 are formed on thefin-shaped structure 14, the SDB structure 18, and the STI 16.Specifically, a dual hard mask structure composed of a hard mask 45 andanother hard mask 46 is disposed on top of the patterned material layer44 in this embodiment, in which the hard mask 45 is preferably made ofsilicon oxide and the hard mask 46 is made of silicon nitride.Nevertheless, according to an embodiment of the present invention, thehard masks 45 and 46 could also be made of different material while thetwo hard masks 45, 46 could be selected from the group consisting ofsilicon oxide and silicon nitride, which are all within the scope of thepresent invention.

Next, at least a spacer 48 is formed on the sidewalls of the each of thegate structures 24, 26, 28, 30, 32, 34, 36, 38, 40, a source/drainregion 50 and/or epitaxial layer (not shown) is formed in the fin-shapedstructure 14 adjacent to two sides of the spacer 48, and selectivesilicide layers (not shown) could be formed on the surface of thesource/drain regions 50. In this embodiment, the spacer 48 could be asingle spacer or a composite spacer, such as a spacer including but notlimited to for example an offset spacer and a main spacer. Preferably,the offset spacer and the main spacer could include same material ordifferent material while both the offset spacer and the main spacercould be made of material including but not limited to for example SiO₂,SiN, SiON, SiCN, or combination thereof. The source/drain regions 50could include n-type dopants or p-type dopants depending on the type ofdevice being fabricated. Next, a selective contact etch stop layer(CESL) (not shown) is formed on the gate structures 24, 26, 28, 30, 32,34, 36, 38, 40 and the STI 16, and an interlayer dielectric (ILD) layer54 is formed on the CESL.

Next, as shown in FIG. 3, a planarizing process such as CMP is conductedto remove part of the ILD layer 54, the hard masks 46, and part of thespacers 48 so that the top surfaces of the hard masks 45 and theremaining ILD layer 54 are coplanar. Next, a patterned mask 56 is formedon the ILD layer 54, in which the patterned mask 56 includes openings58, 60 to expose the top surface of the gate structures 32 and 38. Inthis embodiment, the patterned mask 56 could be a tri-layered structureincluding an organic dielectric layer (ODL), a silicon-containing hardmask bottom anti-reflective coating (SHB), and a patterned resist andthe step of forming the openings 58, 60 in the patterned mask 56 couldbe accomplished by using the patterned resist as mask to remove part ofthe SHB and part of the ODL.

Next, an etching process is conducted by using the patterned mask 56 asmask to remove the hard masks 45 and the patterned material layers 44 ofthe gate structures 32, 38 for forming a first recess 62 exposing theSDB structure 18 and a second recess 64 exposing the STI 16. As shown inFIGS. 2-3, it should be noted that the first recess 62 formed at thisstage is extending along the same direction (such as Y-direction) as theSDB structure 18 underneath while the second recess 64 is formedextending along a different X-direction to divide gate structures 24,26, 28, 30 and gate structures 34, 36, 38, 40 into smaller segments.

It should further be noted that the depths of the first recess 62 andthe second recess 64 could be the same or different depending on thedemand of the SDB structure 18 and STI 16 underneath. For instance, ifthe SDB structure 18 were made of silicon nitride while the STI 16 weremade of silicon oxide, the bottom surface of the first recess 62 formedafterwards could be slightly lower or higher than the bottom surface ofthe second recess 64 depending on the etchant used during the etchingprocess and if both the SDB structure 18 and STI 16 were made of samematerial such as silicon oxide, the bottom surfaces of the two recesses62, 64 would preferably be coplanar.

Next, as shown in FIG. 4, a dielectric layer 66 is formed in the firstrecess 62 and the second recess 64 at the same time to fill the firstrecess 62 and second recess 64 completely. In this embodiment, thedielectric layer 66 could be made of dielectric material including butnot limited to for example silicon dioxide (SiO₂), silicon oxycarbide(SiOC), silicon nitride, or combination thereof.

Next, as shown in FIG. 5, a planarizing process such as CMP is conductedto remove part of the dielectric layer 66, the hard masks 45, and evenpart of the ILD layer 54 and part of the CESL to form another SDBstructure 68 between the gate structures 30, 34 and an isolationstructure 70 on top of the STI 16 and adjacent to the gate structure 36,in which the top surfaces of the SDB structure 68, the isolationstructure 70, and the ILD layer 54 are coplanar.

Preferably, the new SDB structure 68 includes a bottom portion 72embedded within the fin-shaped structure 14 and a top portion 74 on thebottom portion 72. Preferably, the top portion 74 of the SDB structure68, the bottom portion 72 of the SDB structure 68, the isolationstructure 70, and the STI 16 could be selected from the group consistingof SiO₂, SiOC, and SiN while the top portion 74 and the bottom portion72 could be made of same material or different material, the STI 16 andthe isolation structure 70 could be made of same material or differentmaterial, or the STI 16 and the bottom portion 72 of the SDB structure68 could be made of same material or different material.

For instance, the bottom portion 72 of the SDB structure 68 could bemade of silicon nitride while the top portion 74 is made of silicondioxide, the bottom portion 72 could be made of silicon dioxide whilethe top portion 74 is made of silicon nitride or SiOC, both the bottomportion 72 and the top portion 74 could be made of either silicondioxide or silicon nitride, the STI 16 could be made of silicon dioxidewhile the isolation structure 70 is made of silicon nitride, the STI 16could be made of silicon dioxide while the isolation structure 70 ismade of SiOC, the STI 16 could be made of silicon dioxide while thebottom portion 72 is made of silicon nitride and the top portion 74 andthe isolation structure 70 are made of SiOC, or the STI 16 and thebottom portion 72 could be made of silicon dioxide while the top portion74 and the isolation structure 70 are made of silicon nitride or SiOC,which are all within the scope of the present invention.

After the new SDB structure 68 and isolation structure 70 are formed, asshown in FIG. 6, a replacement metal gate (RMG) process is conducted totransform the gate structures 24, 26, 28, 30, 32, 34, 36, 38, 40 intometal gates. For instance, the RMG process could be accomplished byfirst performing a selective dry etching or wet etching process usingetchants including but not limited to for example ammonium hydroxide(NH₄OH) or tetramethylammonium hydroxide (TMAH) to remove the gatematerial layer 44 and even gate dielectric layer 42 from each of thegate structures 24, 26, 28, 30, 32, 34, 36, 38, 40 for forming recesses(not shown) in the ILD layer 54.

Next, a selective interfacial layer 76 or gate dielectric layer (notshown), a high-k dielectric layer 78, a work function metal layer 80,and a low resistance metal layer 82 are formed in the recesses, and aplanarizing process such as CMP is conducted to remove part of lowresistance metal layer 82, part of work function metal layer 80, andpart of high-k dielectric layer 78 to form metal gates. In thisembodiment, the gate structures 30, 34, 36 or metal gates fabricatedthrough high-k last process of a gate last process preferably includesan interfacial layer 76 or gate dielectric layer (not shown), a U-shapedhigh-k dielectric layer 78, a U-shaped work function metal layer 80, anda low resistance metal layer 82.

In this embodiment, the high-k dielectric layer 78 is preferablyselected from dielectric materials having dielectric constant (k value)larger than 4. For instance, the high-k dielectric layer 78 may beselected from hafnium oxide (HfO₂), hafnium silicon oxide (HfSiO₄),hafnium silicon oxynitride (HfSiON), aluminum oxide (Al₂O₃), lanthanumoxide (La₂O₃), tantalum oxide (Ta₂O₅), yttrium oxide (Y₂O₃), zirconiumoxide (ZrO₂), strontium titanate oxide (SrTiO₃), zirconium silicon oxide(ZrSiO₄), hafnium zirconium oxide (HfZrO₄), strontium bismuth tantalate(SrBi₂Ta₂O₉, SBT), lead zirconate titanate (PbZr_(x)Ti_(1-x)O₃, PZT),barium strontium titanate (Ba_(x)Sr_(1-x)TiO₃, BST) or a combinationthereof.

In this embodiment, the work function metal layer 80 is formed fortuning the work function of the metal gate in accordance with theconductivity of the device. For an NMOS transistor, the work functionmetal layer 80 having a work function ranging between 3.9 eV and 4.3 eVmay include titanium aluminide (TiAl), zirconium aluminide (ZrAl),tungsten aluminide (WAl), tantalum aluminide (TaAl), hafnium aluminide(HfAl), or titanium aluminum carbide (TiAlC), but it is not limitedthereto. For a PMOS transistor, the work function metal layer 80 havinga work function ranging between 4.8 eV and 5.2 eV may include titaniumnitride (TiN), tantalum nitride (TaN), tantalum carbide (TaC), but it isnot limited thereto. An optional barrier layer (not shown) could beformed between the work function metal layer 80 and the low resistancemetal layer 82, in which the material of the barrier layer may includetitanium (Ti), titanium nitride (TiN), tantalum (Ta) or tantalum nitride(TaN). Furthermore, the material of the low-resistance metal layer 82may include copper (Cu), aluminum (Al), titanium aluminum (TiAl), cobalttungsten phosphide (CoWP) or any combination thereof.

Referring to FIGS. 7-10, FIGS. 7-10 illustrate a method for fabricatinga semiconductor device along the sectional line AA′ of FIG. 1 accordingto an embodiment of the present invention. As shown in FIG. 7, it wouldbe desirable to follow the fabrication process as disclosed in FIG. 2 tofirst form a SDB structure 18 in the substrate 12 to divide thefin-shaped structure 14 into two portions 20, 22, gate structures 30, 34on the fin-shaped structure 14, and a gate structure 32 directly on theSDB structure 18. Preferably, each of the gate structures 30, 32, 34 iscomposed of a patterned gate dielectric layer 42, a patterned materiallayer 44, and a hard mask 46, a spacer 48 is formed on the sidewalls ofeach of the gate structures 30, 32, 34, a source/drain region 50 and/orepitaxial layer is formed in the fin-shaped structure 14 adjacent to twosides of the spacer 48, and selective silicide layers (not shown) couldbe formed on the surface of the source/drain regions 50. The compositionof each of the spacers 48 and the source/drain region 50 could be thesame as the ones disclosed in the aforementioned embodiment and thedetails of which are not explained herein for the sake of brevity.

After the source/drain regions 50 are formed, instead of forming an ILDlayer to cover the gate structures 30, 32, 34, a mask layer 84 is formedon and around the gate structures 30, 32, 34 and a patterned mask 86such as patterned resist is formed on the gate structures 30, 32, 34 andthe mask layer 84, in which the patterned mask 86 includes an opening 88exposing the hard mask 46 of the gate structure 32 directly on top ofthe SDB structure 18. In this embodiment, the mask layer 84 ispreferably made of bottom anti-reflective coating (BARC), but notlimited thereto.

Next, as shown in FIG. 8, an etching process is conducted by using thepatterned resist 86 as mask to remove the hard masks 45 and 46, thepatterned material layer 44, and the patterned gate dielectric layer 42of the gate structure 32 for forming a recess 90 exposing the SDBstructure 18 underneath. After stripping the patterned resist 86,another etching process is conducted without using additional mask toremove the mask layer 84 or BARC completely and exposing the gatestructures 30, 34 on the fin-shaped structure 14.

After removing the mask layer 84, as shown in FIG. 9, a contact etchstop layer (CESL) 92 is formed in the recess 90 and on the surface ofthe gate structure 30, 34 and the fin-shaped structure 14, and adielectric layer 94 preferably serving as an ILD layer is formed on thegate structures 30, 34 and the CESL 92 to fill the recess 90 completely.Preferably, the CESL 92 is made of dielectric material having stresssuch as but not limited to for example silicon nitride (SiN) or siliconcarbon nitride (SiCN) and the dielectric layer 94 is made of oxides suchas silicon dioxide, but not limited thereto.

Next, as shown in FIG. 10, a planarizing process such as CMP isconducted to remove part of the dielectric layer 94 and part of the CESL92 to form another SDB structure 96 between the gate structures 30, 34,in which the top surfaces of the SDB structure 96 and the dielectriclayer 94 are coplanar.

Preferably, the new SDB structure 96 includes a bottom portion 98embedded within the fin-shaped structure 14 and a top portion 100 on thebottom portion 98, in which a CESL 92 is disposed between the topportion 100 and the bottom portion 98. Similar to the aforementionedembodiment, the top portion 100 of the SDB structure 96 and the bottomportion 98 of the SDB structure 96 could be selected from the groupconsisting of SiO₂, SiOC, and SiN while the top portion 100 and thebottom portion 98 could be made of same material or different material.

After the new SDB structure 96 is formed, a replacement metal gate (RMG)process is conducted to transform the gate structures 30, into metalgates. For instance, the RMG process could be accomplished by firstperforming a selective dry etching or wet etching process using etchantsincluding but not limited to for example ammonium hydroxide (NH₄OH) ortetramethylammonium hydroxide (TMAH) to remove the gate material layer44 and even gate dielectric layer 42 from each of the gate structures30, 34 for forming recesses (not shown) in the dielectric layer 94.

Next, a selective interfacial layer 76 or gate dielectric layer (notshown), a high-k dielectric layer 78, a work function metal layer 80,and a low resistance metal layer 82 are formed in the recesses, and aplanarizing process such as CMP is conducted to remove part of lowresistance metal layer 82, part of work function metal layer 80, andpart of high-k dielectric layer 78 to form metal gates. Similar to theaforementioned embodiment, each of the gate structures 30, 34 or metalgates fabricated through high-k last process of a gate last processpreferably includes an interfacial layer 76 or gate dielectric layer(not shown), a U-shaped high-k dielectric layer 78, a U-shaped workfunction metal layer 80, and a low resistance metal layer 82.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

1. A method for fabricating semiconductor device, comprising: providinga substrate having a fin-shaped structure thereon; forming a singlediffusion break (SDB) structure in the substrate to divide thefin-shaped structure into a first portion and a second portion; forminga first gate structure on the SDB structure; forming an interlayerdielectric (ILD) layer on the first gate structure; removing the firstgate structure to form a first recess; and forming a dielectric layer inthe first recess.
 2. The method of claim 1, further comprising: forminga shallow trench isolation (STI) around the fin-shaped structure;forming a second gate structure on the STI; forming the ILD layer on thefirst gate structure and the second gate structure; removing the firstgate structure to form the first recess and the second gate structure toform a second recess; and forming the dielectric layer in the firstrecess and the second recess.
 3. The method of claim 2, wherein the STIand the SDB structure comprise same material.
 4. The method of claim 2,wherein the STI and the SDB structure comprise different material. 5.The method of claim 2, wherein the STI and the dielectric layer comprisedifferent material.
 6. The method of claim 1, wherein the SDB structureand the dielectric layer comprise different material.
 7. A method forfabricating semiconductor device, comprising: providing a substratehaving a fin-shaped structure thereon; forming a single diffusion break(SDB) structure in the substrate to divide the fin-shaped structure intoa first portion and a second portion; forming a first gate structure onthe SDB structure; forming a mask layer around the first gate structure;removing the gate structure to form a recess; removing the mask layer;and forming a dielectric layer in the recess and on the fin-shapedstructure around the recess.
 8. The method of claim 7, furthercomprising forming a contact etch stop layer (CESL) in the recess and onthe fin-shaped structure after removing the mask layer.
 9. The method ofclaim 8, further comprising forming the dielectric layer on the CESL.10. The method of claim 8, wherein the CESL contacts the SDB structuredirectly.
 11. The method of claim 8, wherein the SDB structure and theCESL comprise different material.
 12. The method of claim 7, wherein theSDB structure and the dielectric layer comprise different material. 13.A semiconductor device, comprising: a gate structure on a fin-shapedstructure; a single diffusion break (SDB) structure adjacent to the gatestructure, wherein the SDB structure comprises: a bottom portion in thefin-shaped structure; and a top portion on the bottom portion, whereinthe bottom portion and the top portion comprise different dielectricmaterials and a bottom surface of the top portion is lower than a topsurface of the fin-shaped structure.
 14. The semiconductor device ofclaim 13, further comprising: a shallow trench isolation (STI) aroundthe fin-shaped structure; and an isolation structure on the STI.
 15. Thesemiconductor device of claim 14, wherein a top surface of the SDBstructure even with a top surface of the isolation structure.
 16. Thesemiconductor device of claim 14, wherein the STI and the isolationstructure comprise different material.
 17. The semiconductor device ofclaim 14, wherein the STI and the bottom portion of the SDB structurecomprise same material.
 18. The semiconductor device of claim 14,wherein the STI and the bottom portion of the SDB structure comprisedifferent material.
 19. The semiconductor device of claim 13, furthercomprising a contact etch stop layer (CESL) between the top portion andthe bottom portion.
 20. The semiconductor device of claim 19, whereinthe CESL is U-shaped.